Sandwich-type radome panel



A. mmm

`lune 9, 1953 E. A. BLACK 2,641,561

SANDWICH-TYPE RADoME PANEL Filed sept. s. 1949 FIBER- GLSS CLOTH n ATAYAAYSSSA GLASS FOAM FIBER-GLASS CLOTH FIG. 2

INVENTOR.

vERK: A. BLACK Wwf/MMM ATTORNEY Patented `lune 9, 1953 UNITED STATES PATENT OFFICE SANDWICH-TYPE RADOME PANEL Eric A. Black, Red Bank, N. J.

Application September 8, 1949, Serial No. 114,631

1 claim. V( c1. 154-453) (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

My invention relates to improvements in sand- A kept in mind. A radar set can measure range very precisely, but in order to measure direction accurately or in other words, to get better bearing discrimination, it is necessary among other things, to use a very narrow radio beam, This means going into the region called microwaves and the use, accordingly, of an antenna whose size is as large as possible. Another advantage of concentrating the beam, is to put more of the energy in the required direction, and so get greater sensitivity.

In general, airborne radar sets present diicult design problems on account of the limitations on size and weight, and also because of the great range of operating conditions which are encountered. Accordingly, it is important to take into account radar-installation problems along with the associated airplane design. One of the problems in such design is to devise for the radar set, a housing or radome which is satisfactory electrically, and which at the same time, meets mechanical requirements. In many installations trouble arose which was traced to the eiect oi the antenna housing on the performance of the antenna. In the nose-type radomes, such as were used in the P-61 installations, the energy reflected by the radome wall comes back to the antenna. Even though the amount of energy thus reiiected may be relatively small, it may have a serious consequence in causing a partial or complete blanking out of certain sectors of the viewing screen. In addition, discontinuities, such as ribs and large reflections from the radome walls, and also from the metal surface of the airplanes, may cause a serious distortion of the radiation pattern of the antenna. The practical result of this may be to cause a marked variation of brightness of a target as the relative position between the target and the radar set changes. In other cases a target might appear to be in a certain direction while actually being in a diierent direction. In

2 the case of large, streamlined radomes, problems arise in obtaining adequate strength with the desired electrical characteristics, while at the same time maintaining a lightweight structure. Another problem resides in design of the radome wall so that reection of the microwaves is a minimum over the range of angles of incidence, in order to obtain maximum range and to decrease pattern-distortion trouble due to large random reflection. The ribs previously used in some radomes to give adequate strength, cannot be allowed in the electrical area owing to pattern distortion which might result.

All of the above is contingent, in the first place, upon the design of the panels making up a popular type of radome which is now more or less conventional. If the designer is restricted to only a small amount of reection from these panels, he can use only a very thin Wall of material of a high dielectric factor. If a material of a lower dielectric constant is employed, a much thicker radome wall is permissible. The molded plywood radomes originally used were unsatisfactory. They were made from plywood impregnated and bonded with phenolic resin. Although satisfactory from the point of view of weathering, the conjunction of high dielectric constant with the relatively thick wall needed for mechanical reasons gave too high a reflection. A non-impregnated plywood with a light phenolic glue line had a lower dielectric constant when dry. However, the high water-absorption of this material resulted in a serious increase of dielectric constant on exposure to rain.

At one time during the development of radome structures, a problem arose where the wall thickness based on mechanical considerations was such as tc give much too great a reflection. This problem was solved by placing a dummy wall inside the outside skin of the radome, and separated from it by a closely controlled distance. By using this double-wall construction, the reflections from the two walls can be made to cancel each other, and thus no power is reiiected back to the antenna, Double-wall construction, however, possesses many disadvantages, one of which is the large number of spacers required to hold the correct spacing between the skins, with the possibility of serious pattern distortion.

With all the foregoing in mind, the obj ect of my invention is to provide an improved sandwichtype radome panel which more nearly complies with all the requirements than do the various constructions proposed heretofore. Specifically, these requirements include low dielectric confront.

For the purpose of illustrating my invention, an embodiment thereof is shown .in the drawing, wherein Fig. l is an enlarged, fragmentary, sectional View, the section being taken on the line l-l in Fig. 2; and

Fig. 2 is a fragmentary, plan view 'of a panel constructed and having the electrical and mechanical characteristics in accordance with my invention.

My improved radome panel comprises outer skins or sheets It and li of uber-glass cloth, interposed between is glass foam I2. For the purpose of reenforcernent, the three-ply assembly is interlaced with cords ill of glass ber. As shown -in the drawing, each of the cords Itis passed through the panel at a suitable angle shown as thirty degrees in Fig. 1 to the respective surfaces thereof, is then run along these surfaces a short distance, which may be about a quarter of an inch, and is then passed again through the panel at an angle to the surfaces. This interlacing process is continued so that each cord weaves back and forth through the panel. Each cord, therefore, is made stiff and secured at all lpoints along its length to the adjacent glass material, thereby giving additional strength and rigidity. As shown more clearly in Eig. l, the reenforcing cords ififorrn truss-like units or lattice girders which are disposed uniformly throughout the panel, as shown in Fig. A2. The relatively high section modulus or impact strength characteristic of my improved construction, is attributable to these truss-like units. Considering just one lof these units, it will be seen that the portions of the fiberglass cloth which constitute the chord members thereof, are under stress when load is applied, the respective parts of the associated cord ll acting as lthe web members ofthe truss or girder. Since the component parts il), il, "l2 and fili are made of the same material, there -is no difference of coefficient i" expansion between adjacent parts to cause separation of the 'plies or laminations with temperature variations, as 'in some of the various panel constructions proposed heretofore.

In constructing my improved panel, the ller or core f2 lof .glass foam may be molded to the desired dimensions. The two sheets or plies llil and 'l-l or liber-.glass cloth are cemented respectively to opposite sides of the glass-foam core or vllen Multiple drills may then be used to drill the holes 'for the 'ber-.glass cords or strands ld, these holes being made of a diameter slightly larger than that of the latter. The cords d'4 are "then threaded 'through the holes. During this step, the 'rcementing material is forced or injected into the holes, whereupon the cords become impregnated, and after hardening of this material lthey become stii. The cementing material, furthermore, binds the'cords to the glass-foam iller o'r core I2. The cords Hl will also be cemented to the fiber-glass cloth where contact is made therewith, tlius forming a shear connection at ythese points. 'The particular angle at which the cords I4 are disposed to the plies or laminations l and l l, and the spacing of the cords from each other, are chosen to be most effective for the stresses and electrical conditions involved.

The truss formation or latticework, formed by the cords lil, may be made to slant in the direction of the anticipated stress. Also', additional cords Ma may be employed, and disposed to vcross the cords Id for the purpose of providing reenforcement for loads applied in different directions. The center lamination or nller I2 can be made very light, since it is not depended upon to take or transmit any stresses such as transverse and longitudinal shear.

My improved construction, furthermore, is not only satisfactory as far as aerodynamic loads are concerned, but it is not susceptible to aromatic aviation fuels. Radomes constructed of my improved panels have relatively high heat and cold resistance, and those of the nose type particularly, are not susceptible to thermal 'collapse when exposed to the sun. Also my novel construction reduces absorption or radar waves, to thereby effect a substantial increase in iii-night radar efficiency. lilly improved radome panels can be made without difficulty Ion a mass-production scale, by the low-pressure molding process.

My novel construction vhas been described as being particuiarly adaptable for radomes, and especially for nose-type radorne's. Any emphasis on this aspect of my disclosure, however, is not to be taken inierentially as a limitation to my claims. Uses other than the one specied can be foreseen. In such cases, any yinodilications to suit particular requirements or conditions, will becoine apparent to those skilled in the art without constituting a departure from the spirit of Ario-y invention, or the scope of the cla-im.

l claim as my invention:

In an ultra-high frequency system in 'which an antenna is lmounted on an airplane, 'a sand-wichtype housing for said antenna comprising two sheets ci fiberglass cloth inspaced and substantially parallel relation with respect to each other, glass foam interposed between said sheets, Vthe thickness of said ber-glass sheets being substantially less than that of `said glass foam providing an electrolnagr'ietic energy Vtransparent housing, and fiber-glass cords reeniorcing panel, each of said cords passing through said panel at lan angle of substantially thirty degrees to the respective surfaces thereof and then running along saidsur'faces a relatively shortfdistance and again passing through said panel at substantially said angle in interlaced `fashion, 'each of said vcords being vsecured at substantially all points `alongfits length to the adjacent glass material, said angle being such that said cords o'iier a minimum of interference `to the passage o'f l-el'ectrornagne'tic energy through said Asheets 'and glass foam.

`ERIC n. BLACK.

References Cited in the -le of this patent UNITED STATES PATENTS Number Name Date 1,942,733 Shaver .Ian.f9, 12934 1,9611823: Goldberg =J une 5, i934 2,114,546 kSlayter Apr. 119,51938 2,137,756 Gould et al Nov. 22, "i938 2,414,125 Rheinfrank Jan. 514, Li947 

